The present invention is directed to radio receivers, and more particularly to a method and device for splitting received radio signals among plural receivers.
A radio system may operate with redundant receivers to increase operational reliability of the system. Often it is beneficial to provide the same signal to several receivers. Typically a primary (or first) receiver and one or more standby (or second) receivers use the same antenna and the received signal is provided to all of the receivers through a splitter or switch. Splitters are generally preferred because switches require time to switch the signal path and are generally less reliable and more expensive.
With reference now to FIG. 1, a conventional radio system with a primary receiver 10 and secondary receiver 12 typically uses a power splitter 14 to direct a portion of a signal received at antenna 16 to secondary receiver 12. However, the splitter and the redirection of the received signal cause power losses which degrade system performance and are desirably avoided. Losses in one path may be reduced by intentionally splitting the signal unequally so that a primary receiver(s) performance is degraded less than that of a secondary receiver(s). If the signal is split 50xe2x80x9450 between the primary and secondary receivers, the splitter loss for each receiver (denoted often the noise figure) would be 3 dB, and if the split were 90-10 the primary receiver noise figure would be 0.5 dB and the secondary receiver noise figure would be 10 dB. The use of high quality factor splitters which do not waste signal energy may further reduce losses.
In the prior art the signal is typically provided to a low noise amplifier in the receiver. A characteristic of low noise amplifiers is that they exhibit poor impedance matches when they are optimized for a low noise figure. The prior art inserts isolators or directional couplers before the low noise amplifier to minimize the undesirable effects of the poor impedance matches. However, these components introduce further losses which degrade system performance.
Accordingly, it is an object of the present invention to provide a novel method and device which splits a received signal while avoiding most of the losses of the prior art, thereby obviating the problems of the prior art.
It is another object of the present invention to provide a novel method and low noise figure power splitter for redundant receivers which eliminates most of the loss prior to the low noise amplifier in which the entire received signal is directed to a low noise amplifier in the primary receiver which is intentionally optimized for low noise (thereby aggravating the impedance mismatch) to cause a usable signal to be reflected, and in which the reflected signal is routed to the remaining receivers for use.
It is yet another object of the present invention to provide a novel method and device in which the normally undesirable mismatch of the noise optimized amplifier in the primary receiver is used to cause a reflection of power to standby receivers.
It is still another object of the present invention to provide a novel method of splitting received signal energy among plural receivers in which received signal energy is provided to a directional circulator (or coupler) which is coupled to a first receiver which reflects a reflected portion of the received signal energy, and in which the reflected portion is directed by the directional circulator (or coupler) to a second receiver for use.
It is a further object of the present invention to provide a novel device for providing a received signal to primary and standby receivers in which a first circulator (or coupler) is coupled to the primary receiver for directing a received signal thereto, the primary receiver having a low noise amplifier having a low return loss so that usable signals are reflected from its input, and in which a second circulator (or coupler) is coupled to the first circulator (or coupler) and to a standby receiver for directing the signal reflected from the low noise amplifier to the standby receiver.
It is yet a further object of the present invention to provide a novel method of splitting received signal energy between a primary and a standby receiver so that when the primary receiver is inoperable otherwise removed, signal energy to the standby receiver is increased.